.course-item { position: relative; float: left;
  margin-left: 23px; margin-top: 22px; width: 222px; height: 125px;}
.shadow { position: absolute; top: 0; left: 0;
  width: 100%; height: 100%; background: rgba(0, 0, 0, 0.5);}
.course-name { position: absolute; font-size: 20px; color: #fff;
  line-height: 36px; top: 50%; left: 0; margin-top: -18px; width: 100%;
  text-align: center; z-index: 2;}
.opt {  /*display: none;*/
  position: absolute; top: 50%; left: 50%;
  margin-top: -17px; margin-left: -70px;
  width: 140px; height: 35px;
  font-size: 14px; line-height: 35px; color: #fff;
  text-align: center; background: #00aae5; border-radius: 4px;}
